This paper underlines the importance of the Pseudo-Aristotelian treatise "De spiritu" for our knowledge of early Hellenistic anatomical and physiological theories. We claim that the treatise verifies reports on certain 4th- and 3rd-century conceptions and debates otherwise attested only in later sources, and offers invaluable information on otherwise unknown ideas and discussions. Our claim is based on ten case-studies in which we explore the relation between the views found in "De spiritu" and known to us from other ancient sources, regarding ten specific topics. Following the results of our case-studies, we argue that De spiritu should be dated to the early decades of the 3rd century BC, after the circulation of the doctrines of Praxagoras of Cos, but before the discovery of the central nervous system by Herophilus and Erasistratus.